Muscle Toning and Development

Q:A number of horses I've seen appear to have asymmetrical muscle development, particularly over the shoulder area, which can make saddle fitting difficult. Many publications seem to say that the larger shoulder indicates that the horse is having to work harder with this leg and that muscle mass has therefore increased--just like with a weight lifter. However, I have also heard that the larger shoulder is actually flaccid muscle, and the contraction of hard-working muscles in the opposite shoulder makes it appear flatter--more like the toned muscles of a sprinter. Which is correct?

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A:Actually, neither might be correct. Developmentally, approximately 80% of horses have a larger, more bulging left shoulder, while 20% have a larger right shoulder. The apparently larger side has the shoulder blade in a position farther back (toward the rear), while the flatter blade is set farther forward. The shoulder joint is also farther forward on the flatter side. The bigger shoulder is usually accompanied by a flatter foot and lower heel, indicating that the horse bears more pressure on the heel, and the farther forward shoulder has a more clubbed foot.

This difference in feet might start at a very young age, as some farriers have noticed that, in grazing foals, the clubby foot is placed back with less weight on the heel, and the flatter foot is forward with more weight on the heels.

In some horses, the larger shoulder becomes a saddle fitting problem and often a movement/performance problem due to muscle pain and tension. In other horses, the differences are slight and do not become a problem. But if you look down the back of 20 horses (standing on a bucket behind the horse), very few will be the same on both sides.

At this time, we think the 80/20 breakdown is caused by a genetic right-hand/left-hand phenomenon, not a learned behavior. Injuries might also cause some asymmetry. There are no bones that hold the shoulder to the horse's body, just muscle. And just as people can carry one shoulder higher than the other just from muscle tension, horses do the same.

So what can you do about this asymmetry? Try to get your horse some body work, acupuncture, chiropractic, good quality massage, and stretching to release the muscle tension and pain. Shoeing also plays a part, as poor shoeing can increase the normal, slight differences in the horse's feet, which will increase the problem up top. Some horses might need help from the foot up by using orthotics, such as adding a pad to only one side. Other horses will rebalance their shoulders and movement with natural balance shoeing, if done properly. Just riding more in one direction will not help.

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